Tumors may have the capacity to subvert host defense mechanisms and thus escape from destruction by the host. Recent studies indicate that this may in part be mediated by soluble factors produced by the tumor cells. Several mouse tumors that we have examined produce a low molecular weight factor which affects macrophages resulting in the modulation of their properties. This research proposal seeks to undertake the functional and biochemical characterization of this factor. The factor(s) will be purified and tested for its effects on macrophages, polymorphonuclear leukocytes and properties of lymphocytes such as proliferative response to mitogens, proliferative response in mixed leukocyte culture reaction, generation of cytotoxic T lymphocytes in mixed leukocyte culture, T cell mediated cytotoxicity and immune response. The macrophage modulating factors produced by different tumors will be examined biochemically and functionally to determine if they are identical in nature. Also, tumor bearing hosts will be examined for the presence of this factor in circulation. In addition, purified factor will be tested for anti-inflammatory effect and effects on antibody response and cell mediated immunity in vivo. The purified factor will conjugated to carriers, the conjugates will be used as immunogens and attempts to raise antiserum against the factor in rabbits will be made so that the antiserum can be used for the estimation as well as neutralization of the factor. Finally, the role of the tumor factor, if any, on tumor-host relation will be examined by studying the effects of independent injections of purified tumor factor and antibody against the factor on the mean survival time of tumor bearing hosts. These in vitro and in vivo studies should provide information on whether and how the tumor factor subverts host defense mechanisms and facilitates the spread of tumor.